I. Field of the Invention
The present invention relates generally to railway car handling or train positioning equipment and, more particularly, to an apparatus for indexing a string of cars through a work station wherein the cars remain coupled. Within this field, the invention further focuses on a drive system for such an indexer which includes automated direct chain tension control which not only enables the chain to be maintained snug in all sprockets and dog carriages to be moved freely with the dogs retracted in a seeking mode in either direction at one force level, but also enables and controls deployment of the dogs and operation of the carriages to move cars in either direction under full load in a second force range.
II. Related Art
Trains of varying lengths, some containing as many a hundred or more cars of various sizes and shapes, have long been acknowledged as desirable and efficient carriers of bulk raw material such as coal, iron ore, limestone, various finely divided dry bulk agricultural produces including grains, etc., and liquid or dry chemicals. These cars are typically filled from above and, while some may be emptied using a rotary car dumper as in the case of coal or iron ore, most and particularly, those carrying agricultural products, are bottom-emptied over stationary freight handling equipment such as chutes, conveyor handlers or the like. Thus, whether being loaded or unloaded, the cars may have to be precisely positioned under or over dedicated filling or receiving facilities situated at fixed stations along the railroad track.
In the discharge operation, a connected train engine roughly positions one end of a string of cars to be unloaded close to the unloading facility. Because train engines are not well suited for indexing or precisely positioning individual cars or even strings of cars along the track, let alone precisely over individual bins, train positioning devices known as railroad car progressors or indexers have been built and operated at fixed stations. Railroad car indexers of the class of interest include at least one car engaging and propelling member or xe2x80x9cdogxe2x80x9d for engaging at least one railroad car in a string or trip of cars and moving the string a given distance along the railroad track. The car engaging members are most often situated and operated along an auxiliary indexer track or guideway juxtaposed in parallel relation to the railroad track in the fixed receiving facility. Many car indexers of the class are operated utilizing chains and sprockets to move carriages carrying train-engaging dogs which may operate against the railroad car bogey frames. Indexers of the class are shown, for example, in U.S. Pat. Nos. 4,354,792, 5,709,153 and 6,267,059. As can be seen from these examples, the dogs may be operated vertically or horizontally to engage the bogey frames or even couplings of the cars of interest.
One long standing problem involved with chain-operated railway car indexer systems involves the inability to maintain continuous proper chain tension. Thus, an initially tight chain, after numerous operations of the indexer system, loosens as parts tend to wear and the chains then become loosely engaged in the sprockets to the point where teeth may be skipped and malfunctions occur. In the past, these problems were addressed by periodically taking the system out of service to remove one or more links from the chain to restore continuity between the chain and all sprockets involved. It would clearly present an advantage in such a system were the chain tension subject to continuous and automated control. It would create an even still further advantage if an automated chain tensioning system could be realized, not only to maintain proper tension in the system in a first or lower force range when the system is utilized to find and engage a railway car, but also in a second or higher force range to deploy dogs to engage and move the cars to the desired position.
The present invention enables a desired tension to be maintained directly from the chain of a chain-operated single direction or reversing railway car indexing system by the provision of a tension regulating system which includes a position-adjustable idler sprocket in conjunction with a controlled operating device with capabilities of producing a plurality of force ranges in the chain which encompass both a dog-retracted idling or car-seeking mode and a dog-deploying car-engaging and positioning mode.
In one embodiment, this system is utilized in conjunction with a two-position carriage-connecting cylinder in a dual-carriage reversing car indexing system in which opposed pivotally-mounted dogs are connected by a fixed length tension linkage through a self-centering spring cylinder in a manner such that extension of the carriage-connecting cylinder produces a corresponding movement in the linkage connections which, in turn, produces pivotal deployment of the opposed dogs. In another embodiment using horizontally pivoting dogs, the linkage between dogs may consist of a single connecting rod.
The pair of consecutive oppositely disposed dog carriages, each carrying an operable car-engaging dog together form a pair of opposite facing or opposed spaced dogs for use in a reversing system, the inward facing carriage ends being connected by the extensible carriage connecting cylinder which is biased to remain in a retracted or collapsed position until the biasing force is overcome. Biasing is preferably accomplished by utilizing a supply of gas-pressurized fluid to maintain the desired force on the cylinder rod end.
The system typically operates in a seeking or idling mode with a chain tension force between 3,000 lbs. (1360.5 kg) and 6,000 lbs (2721 kg) which is sufficient to operate the indexer along the indexing guideway while seeking a railway car with dogs retracted or down and the inter-carriage distance at a minimum. When it is desired to deploy the dogs in moving or in engaging a bogey frame, or the like, the chain force can be increased above the 6000 lbs (2721 kg) threshold necessary to extend the carriage connecting cylinder to its full length at which point it becomes a connecting rod and, at the same time, causes the linkage between the dogs to raise or deploy the dogs.
The spring cylinder used in some embodiments contains internal springs which bias the dogs in a down or retracted position. The self-centering spring cylinder compression springs, however, further compress as required to allow a dog to be downed or pushed back as by contact with an obstruction bogey frame from behind in one direction while allowing the other dog to remain in its extended or raised position. Conversely, the compression springs also compensate transition for the situation in which the system pressure is reduced so that the dogs try to retract, but a dog is held in the raised or deployed position by an external force as by being at the time up against a bogey frame by allowing the unobstructed dog to retract or drop even though the other dog is prevented from retracting until the bogey frame is cleared.